Determination of Free Lime in Steelmaking Slags by Use of Ethylene Glycol Extraction/ICP-AES and Thermogravimetry

Abstract

Steelmaking slags are mainly used as aggregates for road and civil constructions and slag products successfully replace natural sand and macadam. However, the slags may contain appreciable amounts of free lime (CaO) that can cause expansive self-destruction by reactions with water and carbon dioxide in the air. It is thus very important in evaluating the quality of the slags as raw materials to develop an accurate and precise method for determination of free lime in the slags. In the present work we developed a method for determination of free lime in the slags that consists of extraction with ethylene glycol followed by inductively coupled plasma atomic emission spectrometry (ICP-AES) and thermogravimetry (TG). The ethylene glycol extraction method (EG method) has been used as a conventional method for analysis of free lime in steelmaking slags. It has been known, however, that the analytical results obtained by the EG method are not reproducible and ethylene glycol dissolves not only CaO but also Ca(OH)₂. We re-examined the EG method and optimized the conditions for complete extraction of both CaO and Ca(OH)₂ in the slags. We also found that TG enables one to determine Ca(OH)₂ in steelmaking slags. The content of CaO in a slag sample is calculated from the amount of calcium determined by the improved EG method and that of Ca(OH)₂ obtained by TG.